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Fire safety in timber buildings

Technical guideline for Europe

The very fi rst European-wide guideline on the fi re-safe use of wood in buildings

Main results from the WoodWisdom-Net Research project

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During the past hundred years, the average temperature on earth has risen by 0.7°C. The UN’s climate panel has esta-blished that mankind’s emissions of carbon dioxide and other greenhouse gases are the main cause. Combustion of fossil fu-els has brought about a dramatic rise in the level of carbon di-oxide in the atmosphere [IPCC – UN Intergovernmental Panel on Climate Change – Assessment Report, 2000]. Governments throughout Europe and world aim to achieve up to 60 % re-duction in CO2 emissions by 2050. One of the key areas for improvement, not only contributing considerably to CO2 emis-sion levels, but also to our general quality of life, will be the structures in which we live and work. There is better awareness of the issues related to the sustainable design and construction of buildings, which has led to an increased interest in the use of timber.

Forests play a key role in mitigating climate change as they absorb carbon dioxide from the atmosphere and store the car-bon in trees and in the ground. Research shows that cultivating forests and utilizing their resources benefi ts the environment. The combination of active silviculture, using tree tops and branches to produce electricity and thermal energy and manu-facturing of timber products can bring about signifi cant reduc-tions in emissions of carbon dioxide [Swedish University of Agricultural Sciences, 2008].

Increased use of timber in construction is one means of using renewable raw materials and energy from forests that consti-tutes a key aspect to the climate strategy. Wood and paper are climate-friendly alternatives, provided forestry activities are sustainable. More than 80 % of Europe’s forests are managed sustainably, adhering to established and well-policed manage-ment schemes and guidelines. Two main schemes are establis-hed in Europe, namely PEFC and FSC. Both schemes ensure a sustainable healthy yield of wood, while maintaining biologi-cal diversity and replacing harvested stocks [CEI-Bois, Tackle Climate Change, 2006].

Wood products from sustainably managed forests • act as a carbon sink throughout their life,

• have low energy consumption and one of the lowest CO2 emissions of any commonly used building material, • are renewable and

• encourage further forest expansion, increasing the carbon sink effect and reducing the CO2 in the atmosphere.

Part of the answer to the

climate challenge

Reference: CEI Bois “Europe’s forests”

“Forestry practices can make a signifi cant contribution by reducing greenhouse gas emissions through increasing the amount of carbon removed from the atmosphere by the national forest estate, by burning wood for fuel, and by using wood as a substitute for energy-intensive mate-rials such as concrete and steel.”

Securing the Future – UK government strategy for sustai-nable development

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Timber construction

Globally, forests are an immense resource, accounting for about 30 % of the Earth’s total land base. Europe has more than 1,000 million ha of forest spread over 44 countries, equivalent to 1.42 ha (more than two football pitches) per person.

The wood-based sector is one of the main contributors to the European social, economical and environmental set strategies. With an annual production value in EU-25 of some EUR 550-600 billion, the forest-based industries account for about 8 % of the total value added in the manufacturing industry in the EU. Additionally, there are some 16 million private forest ow-ners in Europe owning more than 60 % of the forestland. The sector and related industries provide between 3 and 4 million jobs in industry in the EU, to a large extent in rural areas and in SMEs, constituting one of the EU’s most important and dynamic industrial sectors by representing some 10 % of the EU manufacturing industries. In many regions, this bio-based economy often represents the main source of livelihood. [Eu-ropean Forest Based Sector, 2005]. It has been shown that the increased use of timber can help promote and implement sus-tainability in construction, thereby helping society to mitigate climate change.

Recognizing the importance of wood, a naturally renewable building material is vital for meeting the challenges of climate change and ensuring a sustainable future.

Timber has been a favoured construction material from the be-ginning of civilization because of its abundance, high stiffness and strength-to-weight ratios and the relative simplicity with which it can be adapted to use. These days, timber products have experienced a renaissance as their environmental creden-tials and an industry striving for continuously lower energy and less pollution appeal to consumers in a variety of sectors, from furniture to construction. The highest forest management standards ensure that there is a potential for a continuous and sustainable supply and use of timber as a building material in the future. It is therefore not surprising that timber structures are becoming an important element in sustainable and econo-mic development, and have attracted worldwide attention in recent years.

New construction methods and new design tools have made timber framed houses an effi cient construction method, offe-ring good quality at affordable prices. Construction sites main-ly employing timber products are recognised for their quiet and dry conditions, and the completed buildings offer user-friendly, healthy, natural living environments.

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Fire safety

The combustibility of timber is one of the main reasons that too many building regulations and standards strongly restrict the use of timber as a building material. Fire safety is an important contribution to feeling safe, and an important criterion for the choice of materials for buildings. The main precondition for increased use of timber for buildings is adequate fi re safety. World-wide, several research projects on the fi re behaviour of timber structures have been conducted over about the past two decades, aimed at providing basic data and information on the safe use of timber. Novel fi re design concepts and models have been developed, based on extensive testing. The current improved knowledge in the area of fi re design of timber struc-tures, combined with technical measures, especially sprinkler and smoke detection systems, and well-equipped fi re services, allow safe use of timber in a wide fi eld of application. As a result, many countries have started to revise fi re regulations, thus permitting greater use of timber.

Fire test and classifi cation methods have recently been har-monised in Europe, but regulatory requirements applicable to building types and end users remain on national bases. Alt-hough these European standards exist on the technical level, fi re safety is governed by national legislation, and is thus on the political level. National fi re regulations will therefore re-main, but the new European harmonisation of standards will hopefully also speed up the reform of regulations.

Major differences between European countries have been identifi ed, both in terms of the number of storeys permitted in timber structures, and of the types and/or amounts of vi-sible wood surfaces in interior and exterior applications. Se-veral countries have no specifi c regulations, or do not limit the number of storeys in timber buildings. However, eight storeys are often used as a practical and economic limit for the use of timber structures. This limit may be higher for facades, linings and fl oorings, since these applications may also be used in, for example, concrete structures.

Multifamily houses, Inner harbour, Sundsvall, Sweden.

Multifamily house Rydebäck, Helsingborg, Sweden.

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The FireInTimber project

The WoodWisdom-Net research project FireInTimber was conducted during 2007–2010 in close cooperation with 14 partners in nine countries.

The key objective for the project was to provide new possi-bilities for wood products in construction through proper fi re design. The use of wood products is to be supported and stimu-lated by comprehensive and scientifi cally robust background data, which is presented in user-friendly and adapted tools for engineers and other stakeholders. The programme and its outcome are to facilitate and lead to simplifi ed and quicker approval processes for wood products in buildings. This will increase the general public’s confi dence and positive percep-tion of and about wood products.

The vision is to ensure that the wider use of wood in buildings will be associated with improved fi re safety. The project also built a knowledge base by promoting core competence and multidisciplinary research. The transfer of new knowledge will be enhanced by networking between research and industry.

The FireInTimber project has resulted in new knowledge, es-pecially for modelling of the load-bearing capacity of new ty-pes of timber structures. The project has resulted in about fi fty scientifi c papers, reports and presentations at scientifi c and technical conferences. The main result for a greater audience is the technical guideline Fire safety in timber buildings. It is the very fi rst Europe-wide guideline on the fi re safe use of wood in buildings.

The design guide presents information for architects, engine-ers, educators, authorities and building industries on the fi re safe use of timber structures and wood products in buildings. It aims at providing the highest scientifi c knowledge with regard to fi re safety at the European level. The guidance covers the use of design codes (such as Eurocode 5), European standards, practical guidance and examples for fi re safe design and prin-ciples of performance based design.

The design guide is focusing on structural fi re protection by proving latest detailed guidance on load-bearing and separa-ting functions of timber structures under standard fi re expo-sure. New design methods are presented. They will be used as input for the next revision of Eurocode 5, but can already be used by designers. The guideline includes information on reaction to fi re performance of wood products according to the new European standards. The importance of proper detailing

Main results

Multifamily house Ölzbündt, Dornbirn, Vorarlberg, Austria.

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The Technical guideline

for Europe

Chapter 1; Timber buildings, provides a short introduction to the established uses of timber buildings and the renaissance of timber structures in recent years as a result of the drive towards more sustainable construction solutions.

Chapter 2; Fire safety in buildings, gives an overview of the basic concepts of fi re safety in buildings. It presents informa-tion on fi re behaviour, fi re loads, fi re scenarios and fi re safety objectives. Means of fulfi lling the fi re safety objectives are described for use in all buildings and as a basis for the design solutions in these guidelines.

Chapter 3; European requirements, presents an overview of the new European requirements for fi re safety in buildings based on the Construction Products Directive (CPD) and its essential requirements. These requirements are mandatory for all European countries. They include the classifi cation systems for reaction to fi re of building products, fi re resistance of struc-tural elements, external fi re performance of roofs, fi re protec-tion ability of claddings and structural Eurocodes. Descripprotec-tions of how these requirements are applied to wood products and timber structures are given in the following chapters.

Chapter 4; Wood products as linings, fl oorings, claddings

and façades, presents the reaction-to-fi re performance of

wood products according to the new European classifi cation system. A wide range of products is included: wood-based panels, structural timber, glued laminated timber (gluelam), solid wood panelling and wood fl ooring. A new system for the durability of the reaction-to-fi re performance of wood products is explained and put into context, as well as the recently published K-class system for coverings with fi re protection ability.

In addition to reaction-to-fi re performance, some countries have additional requirements for façade claddings for which no European harmonised solution currently exists. Best prac-tice and state-of the art information on fi re scenarios for faca-des are presented.

Chapter 5; Separating structures, presents the basic requi-rements, calculation methods based on component additive design and the Eurocode 5 design method. It also presents an improved design method from recent research as potential in-put for future revisions of Eurocode 5 and practical examples on how to use the method.

Flashover Furnishing and surface linings (Reaction to fire) Structural elements (Fire resistance) Initial fire Fully developed fire Cooling Time Temperature 1990 2000 2010 2020 (vision)

Design for both the initial and the fully developed fi re in buil-dings is included in the guideline.

Restrictions to use of timber structures in higher buildings, set by national prescriptive regulations, have been eased in Eu-rope over the last decades. A further increase in permitted use is expected.

Short summary of guideline chapters

Fire safety

in timber buildings

Technical guideline

≥ 5 storeys 3-4 storeys

≤ 2 storeys (incl 0) No information Load-bearing structure without sprinklers

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New fi re design models have been developed for new innova-tive timber structures and verifi ed by testing. The new models will be included in next version of Eurocode 5.

Proper detailing in timber structures is necessary to ensure that the fi re resistance of structures is maintained. Fire stops are needed for joints, penetrations and installations.

Chapter 6; Load-bearing timber structures, introduces the design methods for verifi cation of the structural stability of timber structures in the event of fi re, applying the classifi ca-tion for Criterion R for fi re resistance (load-bearing funcca-tion). Reference is made to Eurocode 5 with respect to charring and strength and stiffness parameters. Alternative design models are presented, as well as new design methods for timber struc-tures currently outside the present scope of Eurocode 5. Chapter 7; Timber connections, provides an overview of the basic requirements for timber connections. The calculation methods in Eurocode 5 are complemented with state-of-the-art design methods, the result of recent research. Both timber-to-timber and steel-to-timber-to-timber connections are included. The mo-dels are described and worked examples presented.

Chapter 8; Fire stops, service installations and detailing in

timber structures, deals with the need for adequate detailing

in the building structure to prevent fi re spread within the buil-ding elements to other parts of the builbuil-ding. Special attention is paid to basic principles, fi re stops, element joints and building services installations. Several practical examples of detailing in timber structures are included.

Chapter 9; Novel products and their implementation, is ai-med primarily at product developers. It describes guidelines for introducing novel structural materials and products. The basic performance requirements and potential solutions for insulating materials, encasing claddings and board materials, thin thermal barriers and fi re-retardant wood products are in-cluded. The innovation process from idea to approved product ready for the market is outlined.

Chapter 10; Active fi re protection, describes how such pro-tection is used to achieve a more fl exible fi re safety design of buildings and an acceptable level of fi re safety in large and/or complex buildings. The chapter introduces common active fi re protection systems, including fi re detection and alarm systems, fi re suppression and smoke control systems. Sprinkler installa-tion provides special benefi ts for increased use of wood in buil-dings, particularly where surfaces are to remain visible. Chapter 11; Performance-based design, describes the basic principles of performance-based design, requirements and verifi cation. Fire risk assessment principles are described in terms of objectives, fi re safety engineering design, design fi res, calculation/simulation methods and statistics. A case study of a probabilistic approach is also included.

Chapter 12; Quality of construction workmanship and

in-spection, describes the need for execution and control of

work-manship to ensure that the planned fi re safety precautions are built in. It also emphasises the need for fi re safety at building

New active suppression system Required fi re safety level

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FireInTimber

FireInTimber research partners

Country Partners Contacts E-post

Sweden SP Trätek Birgit Östman, coordinator birgit.ostman@sp.se

Jürgen König jurgen.konig@sp.se

Joachim Schmid joachim.schmid@sp.se

Finland VTT Esko Mikkola esko.mikkola@vtt.fi

Tuula Hakkarainen tuula.hakkarainen@vtt.fi

Germany TUM Technische Universität München Stefan Winter winter@bv.tum.de

René Stein stein@bv.tu-muenchen.de

Norman Werther werther@bv.tu-muenchen.de

DGfH Matthias Krolak matthias.krolak@gmx.de

France BPU Blaise Pascal University Abdelhamid Bouchair bouchair@cust.univ-bpclermont.fr

CSTB Dhionis Dhima dhionis.dhima@cstb.fr

Norway TreSenteret, Wood Centre Harald Landrø harald.landro@tresenter.no

UK BRE Building Research Establishment Julie Bregulla bregullaj@bre.co.uk

Austria HFA Holzforschung Austria Martin Teibinger m.teibinger@holzforschung.at

UIBK Innsbruck University Hans Hartl hans.hartl@uibk.ac.at

TUW Technische Universität Wien Karin Hofstetter karin.hofstetter@tuwien.ac.at

Switzerland ETH Zurich Andrea Frangi frangi@ibk.baug.ethz.ch

Estonia Resand Alar Just ajust@staff.ttu.ee

Supporting public funding organisations are

WoodWisdom-Net Research Programme, jointly funded by national funding organisations: Vinnova and Formas (SE), Tekes (FI), Federal Ministry of Education and Research (DE), Ministère de l´Agriculture (FR), Norges forskningsråd (NO), Forestry Commission (UK), FFG (AT), Lignum (CH) and EMTL (EE).

Supporting industry funding organisation is

European wood industry through BWW Building With Wood represented by Dieter Lechner and Rainer Handl, Die Holzindustrie (AT),

Jan Lagerström, Swedish Forest Industries Federation (SE) and Pekka Nurro, Finnish Forest Industries Federation (FI).

Further information from:

Birgit Östman, SP Trätek, Stockholm Sweden, Coordinator birgit.ostman@sp.se; Phone: +46 10 516 6224

The guideline Fire Safety in Timber buildings has been deve-loped within the European research project FireInTimber (Fire Resistance of Innovative Timber structures). Leading experts and researchers from nine European countries are participating and guarantee its quality and relevance.

The project has been sponsored by national funding organisa-tions within the WoodWisdom-Net Research Programme and by European wood industry represented by the Building With Wood process of Roadmap 2010 within CEI Bois.

In addition, work packages 1-4 have resulted in about fi fty scientifi c papers, reports and presentations published by the research partners.

SP

INFO 2010:15 Illus

trations: BRE, Lignum, proHolz, Swedish Forest Industries, SP

T

References

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